Although the theoretical possibilities for the medical use of laser energy have been recognized for a long time, its practical use has been limited to only a few types of procedures. Typically, the procedures in which laser energy has been used for treatment have been in readily exposed, easily accessible portions of the body, such as the patient's skin and eyes. While it has been suggested for some time that laser energy might be useful in the recanalization of obstructed blood vessels to remove the obstruction from the blood vessel, a satisfactory, practical system has not yet been developed. A major obstacle in the development of techniques for applying laser energy to blood vessels has been in the problem of how to deliver the laser beam precisely to the vascular site to be treated and then, how to apply controllably the laser beam so as to remove the biological material causing the blockage without damaging or otherwise adversely affecting the patient's vasculature. The difficulties presented have been compounded further by the dimensional limitations which must be imposed on any catheter which is to be inserted into a blood vessel, particularly narrow blood vessels such as coronary arteries which may have lumens of the order of 1.5 to 4.5 millimeters in diameter.
Among the difficulties is the manner of placing and locating the distal end of the catheter so that it is positioned properly with respect to the obstruction Prior proposals, which have included the use of supplemental optical fibers to transmit illuminating light into the blood vessel in conjunction with other groups of fibers to permit visual observation of the interior of the blood vessel, are not practical because they are too large and too stiff for use in narrow arteries. Another difficulty which has been presented is that there often may be materials such as blood, in the region between the emission point of the laser beam at the end of the fiber and the obstruction. Such material may obstruct the optical path. The blood may become charred at the distal emitting tip of the fiber which can result in overheating and destruction of the optical fiber. Still another difficulty is that such a catheter which is to be advanced to small, distally located arteries must be very flexible to be able to make sharp, short radius bends in order to reach those arteries. The catheter also must have a small diameter, yet must be capable of being pushed and manipulated, from its proximal end, without becoming bunched up or bent as it advances within the patients blood vessels. A further, very desirable feature of such a catheter is that it should be capable of providing fluid communication from the proximal to the distal end of the catheter, to enable liquid infusion or to make pressure measurements. The development of a practical catheter which achieves the foregoing objects while avoiding the above and other difficulties has proved to be a substantial problem.
Although many laser catheters have been proposed in the past, none has proved to be usable to any practical degree. All suffer from one or more of various difficulties. It is among the general objects of the invention to provide a practical and effective catheter system by which laser energy can be delivered to selected sites in a patient's blood vessels with precision and control.